To test the effect of long-term alendronate treatment on skeletal retention of alendronate, 12 postmenopausal osteopenic women will be randomized to alendronate 10 mg daily or placebo, and skeletal retention of 14C-alendronate will be determined pretreatment and after 12 months of therapy. Plateau effect of alendronate will be determined by markers of bone turnover.